Publication U.S. Pat. No. 6,184,633 (Kramer) demonstrates the advantages which result when the lamp voltage of a high-pressure discharge lamp (also referred to for short as lamp below) has a time characteristic which makes use of acoustic resonances in the lamp. This essentially entails a longitudinal resonance in the lamp being excited as a result of amplitude modulation of the lamp voltage and this resonance counteracts undesired demixing processes in the plasma in the lamp. It is even possible for the shape of the plasma, such as constrictions and straight sections, for example, to be influenced in a targeted manner. In addition, it is possible for other resonances, which are not affected by the amplitude modulation, to be suppressed or only sporadically excited by frequency modulation of the lamp voltage. The abovementioned publication describes the effects referred to, but there is no indication as to how the required waveform of the lamp voltage is produced in a cost-effective manner. For the purposes of research, function generators and power amplifiers are available for producing complex voltage waveforms. Such components are, however, not practicable for users of the lamps in question and are not acceptable for reasons of cost. Instead, an operating device is required for commercial applications which, in combination with the lamp, constitutes a cost-effective lighting system.